The invention relates to an electromagnetic actuator having a single armature plunger that reciprocally shuttles between two magnetic paths. The invention affords optimal utilization of the magnetic circuit, including cancellation of undesired retarding-flux in overlapping linkage paths, resulting in increased net magnetic force and faster plunger operation.
In one desirable aspect of the invention, non-magnetic spacers may be eliminated. The nonmagnetic spacers may otherwise be needed for producing reluctance to control the ratio between two magnetic flux path forces. This control is necessary to insure that the dominant magnetic force is in the intended direction of plunger movement.
Another desirable aspect of the invention is its three-wire control capability, eliminating the need for two dedicated wires for each magnetic path.
A pair of coils are energizable to create magnetic fluxes having portions of their linkage paths in common, including through the plunger. When either coil is energized, a primary flux path is created around that coil through the plunger, and a secondary flux path is created around both coils through the plunger. The primary flux attracts the plunger to close a first gap, and the secondary flux attracts the plunger in the opposite direction to maintain a second gap closed.
In accordance with the preferred embodiment of the invention, current to the energized coil is also supplied through a current limiting resistor to the other coil to generate reverse polarity flux around the latter opposing the noted secondary flux in cancelling relation. This reduces or eliminates the retarding-flux in the closed gap and enables the plunger to rapidly move under the influence of the noted primary flux in the open gap.